concentrations. The next level of interest is how much of the cod in each of these categories is dissolved or soluble, and how much is particulate, comprised of colloidal and suspended solids. The nonbiodegradable soluble COD(nbsCOD) will be found in the activated-sludge effluent, and nonbiodegradable particulates will contribute to the total sludge production Because the nonbiodegradable particulate COD(nbpCOD)is organic material, it will also contribute to the VSs concentration of the wastewater and mixed liquor in the activated-sludge process, and is referred to here as the nonbiodegradable volatile suspended solids(nbVSS). The influent wastewater will also contain nonvolatile influent suspended solids that add to the MLSS concentration in the activated-sludge process. These solids are influent inert TSS (iTSS)and can be quantified by the difference in influent wastewater TSS and VSS concentrations For biodegradable COD, understanding the fractions that are measured as soluble, soluble readily biodegradable COd(rbCOD), and particulate is extremely important for activated -sludge process design. The rbCod portion is quickly assimilated by the biomass, while the particulate and colloidal COD must first be dissolved by extracellular enzymes and are thus assimilated at much slower rates Tab. 7-I Biological Effect of rbCOD processes affected by Activated-sludge aeration For plug How or staged aeration zones, there will be a Monk with a readily biodegradable hic igher fraction of rbCoD in the inn COD(rbCOD)concentration Biological nitrogen removal For the preanoxic tank, there will be a higher in influent wastewater influent COD. Can result in smaller anoxic tank volu Biological phosphorus rem Greater infuent rbCoD concentration results in a greater amount of biological phosphorus removal Activated-sludge selector coD fraction of rbCoD in influent COD provides more greater impact on improving sludge volume index(SVI) The rbCoD fraction of the Cod has a direct effect on the activated-sludge biological kinetics and process performance Process applications where the rbCoD concentration affects the process design and erformance are summarized in Table 7-1 The rbCoD consists of complex soluble COd that can be fermented to volatile fatty acids(VFAs)in the influent wastewater. Wastewaters that are more septic, for example, from collection systems in warm climates with minimal slopes, will contain higher concentrations of VF Nitrogenous Constituents. The total Kjeldahl nitrogen(TKN) is a measure of the sum of the ammonia and organic nitrogen About 60 to 70 percent of the influent tKn concentration will be as NH4-N, which is readily available for bacterial synthesis and nitrification. Organic nitrogen is present in both soluble and particulate forms, and some portion of each of these is nonbiodegradable. The particulate degradable organic nitrogen will be removed more slowly than the soluble degradable organic nitrogen because a hydrolysis reaction is necessary first. The nondegradable organic nitrogen is assumed to be about 6 percent of the nondegradable vss as Cod in the influent wastewater( Grady et al., 1999). The particulate nondegradable nitrogen will be captured in the activated-sludge floc and exit in the waste sludge, but the oluble nondegradable nitrogen will be found in the secondary clarifier effluent. The soluble nondegradable nitrogen contributes to the effluent total nitrogen concentration and is a small fraction of the influent wastewater TKn concentration(<3 percent). The soluble nondegradable organic nitrogen concentration in domestic wastewater typically ranges from l to 2 mg/L as N Alkalinity. Alkalinity concentration is an important wastewater characteristic that affects the performance of biological nitrification processes. Adequate alkalinity is needed to achieve complete nitrification Measurement Methods for Wastewater Characterization Readily Biodegradable COD. The rbCoD concentration is either determined from a biological response or estimated by a physical separation technique In the biological response method the oxygen uptake rate (OUR) is followed and recorded with time after mixing the wastewater sample with an acclimated activated-sludge sample. The wastewater may be preaerated so that upon contact with th activated sludge a high DO concentration is present to allow an immediate measurement of the OUR. The wastewater sample and activated sludge are mixed in a batch reactor with separate aeration and mixing 7-47-4 concentrations. The next level of interest is how much of the COD in each of these categories is dissolved or soluble, and how much is particulate, comprised of colloidal and suspended solids. The nonbiodegradable soluble COD (nbsCOD) will be found in the activated-sludge effluent, and nonbiodegradable particulates will contribute to the total sludge production. Because the nonbiodegradable particulate COD (nbpCOD) is organic material, it will also contribute to the VSS concentration of the wastewater and mixed liquor in the activated-sludge process, and is referred to here as the nonbiodegradable volatile suspended solids (nbVSS). The influent wastewater will also contain nonvolatile influent suspended solids that add to the MLSS concentration in the activated-sludge process. These solids are influent inert TSS (iTSS) and can be quantified by the difference in influent wastewater TSS and VSS concentrations. For biodegradable COD, understanding the fractions that are measured as soluble, soluble readily biodegradable COD (rbCOD), and particulate is extremely important for activated-sludge process design. The rbCOD portion is quickly assimilated by the biomass, while the particulate and colloidal COD must first be dissolved by extracellular enzymes and are thus assimilated at much slower rates. The rbCOD fraction of the COD has a direct effect on the activated-sludge biological kinetics and process performance.Process applications where the rbCOD concentration affects the process design and performance are summarized in Table 7-1. The rbCOD consists of complex soluble COD that can be fermented to volatile fatty acids (VFAs) in the influent wastewater. Wastewaters that are more septic, for example, from collection systems in warm climates with minimal slopes, will contain higher concentrations of VFAs. Nitrogenous Constituents. The total Kjeldahl nitrogen (TKN) is a measure of the sum of the ammonia and organic nitrogen. About 60 to 70 percent of the influent TKN concentration will be as NH4-N, which is readily available for bacterial synthesis and nitrification. Organic nitrogen is present in both soluble and particulate forms, and some portion of each of these is nonbiodegradable. The particulate degradable organic nitrogen will be removed more slowly than the soluble degradable organic nitrogen because a hydrolysis reaction is necessary first. The nondegradable organic nitrogen is assumed to be about 6 percent of the nondegradable VSS as COD in the influent wastewater (Grady et al., 1999). The particulate nondegradable nitrogen will be captured in the activated-sludge floc and exit in the waste sludge, but the soluble nondegradable nitrogen will be found in the secondary clarifier effluent. The soluble nondegradable nitrogen contributes to the effluent total nitrogen concentration and is a small fraction of the influent wastewater TKN concentration (<3 percent). The soluble nondegradable organic nitrogen concentration in domestic wastewater typically ranges from 1 to 2 mg/L as N. Alkalinity. Alkalinity concentration is an important wastewater characteristic that affects the performance of biological nitrification processes. Adequate alkalinity is needed to achieve complete nitrification. Measurement Methods for Wastewater Characterization Readily Biodegradable COD. The rbCOD concentration is either determined from a biological response or estimated by a physical separation technique. In the biological response method the oxygen uptake rate (OUR) is followed and recorded with time after mixing the wastewater sample with an acclimated activated-sludge sample. The wastewater may be preaerated so that upon contact with the activated sludge a high DO concentration is present to allow an immediate measurement of the OUR. The wastewater sample and activated sludge are mixed in a batch reactor with separate aeration and mixing. Tab. 7-1 Biological processes affected by readily biodegradable COD(rbCOD) concentration in influent wastewater